Abstract
Proteins that act as global transcriptional regulators play key roles in bacterial adaptation to new niches. These proteins recognize multiple DNA sites across the bacterial genome by different mechanisms. Enterococcus faecalis is able to survive in various niches of the human host, either as a commensal or as a leading cause of serious infections. Nonetheless, the regulatory pathways involved in its adaptive responses remain poorly understood. We reported previously that the MafR protein of E. faecalis causes genome-wide changes in the transcriptome. Here we demonstrate that MafR functions as a transcription activator. In vivo, MafR increased the activity of the P12294 and P11486 promoters and also the transcription levels of the two genes controlled by those promoters. These genes are predicted to encode a calcium-transporting P-type ATPase and a QueT transporter family protein, respectively. Thus, MafR could have a regulatory role in calcium homeostasis and queuosine synthesis. Furthermore, MafR recognized in vitro specific DNA sites that overlap the −35 element of each target promoter. The MafR binding sites exhibit a low sequence identity, suggesting that MafR uses a shape readout mechanism to achieve DNA-binding specificity.
Highlights
Global transcriptional regulators play crucial roles during bacterial adaptation to specific niches
By quantitative RT-Polymerase chain reaction (PCR) assays and using the comparative CT method[15], we determined the relative expression of the regulatory mafR gene in cells grown under laboratory conditions (Brain Heart Infusion (BHI) broth, 37 °C, without aeration) to both logarithmic and stationary phases
OG1RF_12294 has sequence similarity (∼53–56%) to several prokaryotic proteins characterized as calcium P-type ATPases (Supplementary Table S1)[21,22,23,24,25]
Summary
Global transcriptional regulators play crucial roles during bacterial adaptation to specific niches. Genome-wide microarray assays showed that MafR is involved in global regulation of gene expression[5] In such experiments, the transcriptional profiles of strains OG1RF (wild-type) and OG1RF∆mafR (mafR deletion mutant) were compared, demonstrating that MafR activates, directly or indirectly, the expression of at least 87 genes. Compared to OG1RF, the OG1RF∆mafR strain was shown to induce a lower degree of inflammation in the peritoneal cavity of mice Because of these findings, we proposed that MafR could facilitate the growth of E. faecalis in particular human niches and, could contribute to its potential virulence[5]. We hypothesized that MafR, and most likely the regulators of the Mga/AtxA family, recognizes structural features in its target DNAs rather than specific nucleotide sequences[4] Verification of this hypothesis requires the identification of additional MafR binding sites across the bacterial genome. It supports that MafR might recognize particular DNA shapes
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